Method of imparting a false twist to a thermoplastic ribbon

ABSTRACT

A method is provided for imparting a false twist to a thermoplastic, monofilament ribbon, i.e., a monofilament which has a substantially rectangular cross-section and a width to thickness ratio of at least 3 to 1. According to the method, the ribbon is twisted several times and passed over a hot surface and both ends of the ribbon are held under pressure thus retaining the twists on the surface. As the ribbon passes over the surface it is heated on a first side, a first edge, a second side and a second edge in that order, imparting differential orientation to the heated portions which results in a ribbon having a false twist or curl. These ribbons are useful in the fabrication of synthetic turf giving a high bulk effect thereto.

United States Patent Silverman 151 3,681,912 [451 Aug. 8, 1972 [54] METHOD OF IMPARTING A FALSE TWIST TO A THERMOPLASTIC RIBBON [72] Inventor: Bernard Silverman, 2405 Wentworth Street, Raleigh, NC.

[22] Filed: Nov. 12, 1970 [21] Appl. No.: 88,626

[52] US. Cl. ..57/157 TS, 57/167 3,537,252 11/1970 Gilmore et al ..57/167 X 3,548,581 12/1970 Bobkowicz etal ..57/157TSX I Primary Examiner-Donald E. Watkins Attorney-Russell E. Weinkauf, John D. Upham and Neal E. Willis ABSTRACT A method is provided for imparting a false twist to a thermoplastic, monofilament ribbon, i.e., a monofilament which has a substantially rectangular cross-section and a width to thickness ratio of at least 3 to 1. According to the method, the ribbon is twisted several times and passed over a hot surface and both ends of the ribbon are held under pressure thus retaining the twists on the surface. As the ribbon passes over the surface it is heated on a first side, a first edge, a second side and a second edge in that order, imparting differential orientation to the heated portions which results in a ribbon having a false twist or curl. These ribbons are useful in the fabrication of synthetic turf [56] References Cited UNITED STATES PATENTS 2,812,782 11/1957 Stevens ..57/140J UX 3,017,686 l/1962 Breen et al. ..57/140 J UX 3,444,683 5/ 1969 Hesenbruch ..57/ 167 X 3,496,715 2/1970 Fitton ..57/157 MS X giving a high bulk efl'ect thereto.

5 Claims, 3 Drawing Figures -lliiill11lilll.

PATENTEDAUB 8l972 3.681812 FIG. I.

8 VIIIIIIflI/IJIIIIIIIIIIIIIIA 9 FIG. 2.

INVENTOR. BERNARD S/L RMAN BY M ATTORNEY WTHOD OF IMPARTING A FALSE TWIST TO A THERMOPLASTIC RIBBON Recently, artificial turf or grass has exhibited rather wide acceptance as a substitute for natural grass or as heavy use decorative patio or ground coverings. One type of such artificial turf that has performed particularly well is made with a pile of thermoplastic monofilament ribbons which are tufted, woven or knitted into a backing and is described in more detail in US. Pat. No. 3,332,828.

When the term monofilament thermoplastic ribbon is used herein, it is intended to denote a monofilament which has a width at least three times its thickness and a substantially rectangular cross-section. It has been found that in order for the artificial turf product to perform effectively the ribbons used as pile should have a denier above 250, preferably above 300. Among the thermoplastic materials suitable for the process of this invention are polyarnides, e.g. nylon; polyolefins, e.g., polypropylene; polyesters, e.g., polyethelene terephthalate, and other like thermoplastics.

It is of course desirable to produce an artificial turf that has a pile density sufficiently high to simulate the appearance of natural grass. When the product is to be used as a patio or lawn surface, which use does not require the pile density of surfaces used for very heavy duty such as football, it would be especially desirable to ring on the surface which in turn is dependent on the desired degree of false twist. In order to more clearly illustrate the path of the ribbon over heated surface 4, FIG. 3 shows side 6 cross-hatched and side 9 darker than side 8. It can be seen that the ribbon is thus heated in a curled or twisted condition by alternately heating the sides and edges. Therefore, when the ribbon is removed from collection means 5 and the tension thereon is released, the ribbon assumes a curled configuration.

For example, in the construction of a tufted, cut pile' fabric the ribbon is fed from a creel. While on the creel the ribbon is in a flat form which is made possible by maintaining tension on the ribbon as it is mounted on the creel from, e.g., collection means 5. The synthetic turf fabric is constructed by forming loops with the ribbon which are then cut. When the loops are cut, the tension is released and the ribbons adopt a curled configuration which results in a fabric having the appearance of high bulk and pile density.

It should be emphasized that it is important in the process of this invention that sufiicient tension be applied on the ribbon by pressure rolls 3 and 3a. If the pressure applied by these rolls is too little, the twists will not remain on the heated surface but will pass under the roll 3a and onto collection means 5. For purposes of describing the invention it can be said that the pressure applied to the ribbon is sufiicient to maintain reduce the amount of ribbon per unit of surface and yet the twists on the heated surface.

retain the appearance of high density product. It has been found that this can be accomplished by treating the ribbon, prior to its introduction into the artificial turf product, so as to increase its bulk properties.

In accordance with this invention there is provided a process for imparting a false twist to a thermoplastic monofilament ribbon which comprises twisting the ribbon, continuously passing the twisted ribbon over a surface heated to a temperature above about 80 C. and below the melting point of the thermoplastic, applying tension to the moving ribbon on both ends of the heated surface sufficient to maintain the twists on the heated surface and collecting the ribbon.

The invention will be more clearly understood with reference to the accompanying drawing wherein,

FIG. 1 is a side perspective view of suitable apparatus for carrying out the process of this invention;

FIG. 2 is a cross-section view of a ribbon useful in the process of this invention and FIG. 3 is a top view of that portion of FIG. 1 designated by lines 3-3.

In the drawings, ribbon 1 from source 2 is passed under roller pin 3 and over a hot shoe 4 heated, by means not shown, to the desired temperature. Prior to passing the ribbon under roller pin 3a, the ribbon is twisted so that the twist points occur on the heated shoe. The ribbon then is passed under pin 3a and on to collection means 5.

For ease in visualizing what occurs during the process of this invention FIG. 2 shows a cross-section of a monofilament ribbon having sides 6 and 7, and edges 8 and 9, and FIG. 3 illustrates the configuration of the ribbon as it passes over the heated surface 4.

As can be seen from FIG. 3, the ribbon passes over heated surface 4 with alternating sides and edges coming in contact with the surface. The ribbon is thus heated alternately on side 6, edge 8, side 7, edge 9, and so forth depending on the number of twist points occur- The temperature of the heated surface is critical only to the extent that it is sufficient to obtain the desired results and insufficient to melt the thermoplastic. It has been found that temperatures as low as about C. can be used for some thermoplastics. The preferred heating range is between about C. and C.

The amount of twist, or the number of twist points'on the heated surface is of course dependent on the desired amount of false twist in the final product. Anywhere from about one to five turns per inch has been found to give a product with the desired bulk.

The process of this invention may conveniently be carried out during the ribbon orientation step. That is, after the ribbon is extruded it must be drawn to give it the desired strength. This drawing can be accomplished while imparting a false twist according to this invention by merely running collection means 5 at a speed faster than feed source 2. Of course the invention may also be carried out on pre-drawn ribbons.

What I claim is:

1. A process for imparting a false twist to a thermoplastic monofilament ribbon, said ribbon having a denier greater than 250 and a width to thickness ratio of at least 3 to l, which comprises twisting the ribbon, continuously passing the ribbon over a surface heated to a temperature above about 80 C. and below the melting point of the thermoplastic, applying tension to the ribbon on both ends of the heated surface suflicient to maintain the twists on the surface and thereafter collecting the ribbon.

2. A-process according to claim 1 wherein the ribbon is collected under tension sufficient to maintain it in a fiat condition.

3. A process according to claim 1 wherein the temperature of the surface is between 90 and 130 C.

4. A process process according to claim wherein wherein the thermoplastic is nylon.

5. A process according to claim 1 wherein the thermoplastic is polypropylene. 

1. A process for imparting a false twist to a thermoplastic monofilament ribbon, said ribbon having a denier greater than 250 and a width to thickness ratio of at least 3 to 1, which comprises twisting the ribbon, continuously passing the ribbon over a surface heated to a temperature above about 80* C. and below the melting point of the thermoplastic, applying tension to the ribbon on both ends of the heated surface sufficient to maintain the twists on the surface and thereafter collecting the ribbon.
 2. A pRocess according to claim 1 wherein the ribbon is collected under tension sufficient to maintain it in a flat condition.
 3. A process according to claim 1 wherein the temperature of the surface is between 90* and 130* C.
 4. A process process according to claim wherein wherein the thermoplastic is nylon.
 5. A process according to claim 1 wherein the thermoplastic is polypropylene. 